Is this sentence grammtical?
"That girl, in a blue dress, was wearing a red dress yesterday."

Can i use it instead of

"That girl, who is now in a blue dress, was wearing a red dress yesterday."

Question

Is this sentence grammtical?
"That girl,  in a blue dress, was wearing a red dress yesterday."

Can i use it instead of

"That girl, who is now in a blue dress, was wearing a red dress yesterday."

Answer

I think both are grammatically correct although, I prefer the first one. 

"That girl in a blue dress was wearing a red dress yesterday." 

take note that a 'break' or a 'pause' (i.e. comma) are not necessary here. 

"that girl" = Subject 
"in a blue dress" = Adjective Clause 
"was wearing" = Verb 
"a red dress" = Object 

... and these what grammar should comprise of. 

:)

Answer

I agree with Romulus. 
And it would sound even better to say, "That girl in THE blue dress was wearing...."